AP Photo

The tactics of today's insurgent bombmakers are the product of a long-simmering melting pot of global terrorism. Photo: Tom Schierlitz; IED models: Based on actual bombs constructed by Prop House Weapons Specialists Ltd.

One afternoon at the end of March, inside a cinder-block bunker on a small island in Chesapeake Bay, Scott Schoenfeld is waiting to blow something up. On a video monitor in front of him is a grainy image of a rusty steel box about 20 yards away. Inside is an explosive charge and an experimental target. A big, soft-spoken computational scientist wearing a black polo shirt, jeans, and wraparound sunglasses, Schoenfeld is one of the chief armor researchers for the Joint Improvised Explosive Device Defeat Organization, or Jieddo, the Pentagon...